weekend, in one american city, thousands of people are now being notified that they must be tested for hiv and other dangerous diseases because they trusted their dentist. 7,000 people reeling from the news in oklahoma. And for the first time, we're hearing from some of them tonight. Abc's chief medical editor dr. Richard besser tracking the story. Reporter:7,000 patients that sought treatment at this dentist office worrying they may have contracted hepatitis of hiv. Linda grimm is one of them. A news break came on the radio and it was about a dentist and dirty equipment and then at the end they gave his name and i just went -- what? Real loud. I could not believe it. Reporter: Grimm told us dr. Scott harrington's office wasn't like other dentist's she'd been to. Usually they are well lit. There are lots of people. They're friendly. It was very -- you didn't see that many people. Reporter: Today, the health department sent grimm and thousands of other patients this letter, urging them to get screened for hepatitis c, b and hiv. With this note. We understand this news may be alarming to you. Dr. Harrington didn't answer our calls. Health officials found multiple sterilization issues, cross contamination issues and drugs that had expired more than two decades ago. There's no stan ard for dental health, so, when up go to the dentist, keep your eyes open. Three quick things to look for. Is the room clean? Are there barriers on any surface someone is going to touch? And are your instruments in a sealed bag? The most important inspection may be the one you do yourself. And rich is here now. So, rich, you say, there's a question to be sure to ask. Reporter: There is. But first, this is really rare. Dentists take this seriously. But when you're at your dentist office, in addition to looking around, ask them, what are you doing to make sure you're not spreading infection around your office? And a good dentist will be happy to show you.

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